Homogeneous Charge Compression Ignition (HCCI) engine is expected as means for realizing a fuel efficiency as high as the diesel engine while maintaining the low emission characteristics inherent in the gasoline engine. Note that fuel is supplied by injection near the compression top dead center in a normal diesel engine, whereas fuel is injected earlier into a combustion chamber or mixed with air in an intake port and introduced into a combustion chamber, and then the premixed gas is auto-ignited near the compression top dead center by combustion reaction at a compression temperature in the HCCI engine.
The present inventor has considered that it is important to control an internal EGR amount and realize supercharging without a supercharger in order to widen the operation range of the HCCI engine, and proposed the method therefor.
Though the operation range of the HCCI engine can be widened by the above-described method, practical HCCI operation cannot be realized because the rate of pressure rise is too high in the high load operation range. As means for decreasing the rate of pressure rise to realize combustion as slow as the normal spark ignition engine, stratification of the mixed gas and temperature distribution is regarded as effective (see Non-patent Document 1).    [Non-patent Document 1] JSAE20055667